Posture-related modulation of cortical excitability in the tibialis anterior muscle in humans.

Corticospinal excitability in the lower leg muscles is enhanced during standing as compared to other postures. In the present study, we investigated how the excitability of intracortical circuits that control the tibialis anterior muscle (TA) is modulated during standing. Short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were assessed by the paired-pulse transcranial magnetic stimulation technique during standing (STD) and sitting (SIT) with a comparable background activity level in both the soleus and the TA muscle. The results demonstrated that SICI was less effective during STD than during SIT, whereas ICF was more effective during STD than during SIT. These findings suggest that the excitabilities of these cortical neural circuits are modulated depending on posture. A decrease in SICI and an increase in ICF may reflect subliminal enhancement of the cortical excitability in the TA muscle during standing as compared with that during sitting.

Orofacial muscular activity and related skin movement during the preparatory and sustained phases of tone production on the French horn.

This study investigated activity of the embouchure-related orofacial muscles during pre- and postattack phases of sound production by 10 trained French-horn players. Surface electromyogram (EMG) from five selected facial muscles, and related facial skin kinematics were examined in relation to pitch and intensity of a tone produced. No difference in EMGs and facial kinematics between the two phases was found, indicating importance of appropriate formation of preattack embouchure. EMGs in all muscles during the postattack phase increased linearly with an increase in pitch, and they also increased with tone intensity without interacting with the pitch effect. Orofacial skin movement remained constant across all pitches and intensities except for lateral retraction of the lips during high-pitch tone production. Contraction of the orofacial muscles is fundamentally isometric by which tension on the lips and the cheeks is regulated for flexible sound parameter control.

Relationship between muscle cocontraction and proficiency in whole-body sensorimotor synchronization: a comparison study of street dancers and nondancers.

In this study, we investigated muscle cocontraction during a street dance movement task to provide evidence that the level of muscle cocontraction is associated with degree of proficiency in whole-body sensorimotor synchronization movement. Skilled street dancers and nondancers were required to synchronize a knee-bending movement in a standing position to a metronome beat. The dancer group showed significantly smaller variability of temporal deviation (defined as the peak knee-flexion time minus beat onset time), and lower level of muscle cocontraction analyzed by electromyographic data of the agonist and antagonist muscles of the upper and lower leg than did the nondancer group. In addition, multiple regression analyses revealed that the group effect significantly predicted the level of muscle cocontraction. These results show that the level of muscle cocontraction in the lower limbs during whole-body sensorimotor synchronization movement is associated with the degree of proficiency of the movement.

Aging effects on posture-related modulation of stretch reflex excitability in the ankle muscles in humans.

The purpose of this study was to examine the effects of aging on posture-related changes of the stretch reflex excitability in the ankle extensor, soleus (SOL), and flexor, tibialis anterior (TA) muscles. Fourteen neurologically normal elderly (mean 68±6years) and 12 young (mean 27±3years) subjects participated. Under two postural conditions, upright standing (STD) and sitting (SIT), stretch reflex electromyographic (EMG) responses in the SOL/TA muscle were elicited by imposing rapid ankle dorsi-/plantar-flexion. Under the SIT condition, subjects were asked to keep the SOL background EMG level, which is identical to that under the STD condition. In the SOL muscle, both groups showed significant enhancement of the short-latency stretch reflex (SLR) response when the posture changed from SIT to STD. In the TA muscle, the young group showed significant enhancement of the middle- (MLR) and long-latency stretch reflex (LLR) when the posture changed from SIT to STD; no such modulation was observed in the elderly group. Since the TA stretch reflex responses under the STD condition were comparable in the young and elderly groups, the lack of posture-related modulation of the TA muscle in the elderly group might be explained by augmented stretch reflex excitability under the SIT condition. The present results suggest that the (1) SOL SLR responses are modulated both in the young and elderly subjects when the posture is changed from SIT to STD, (2) TA MLR and LLR responses are not modulated in the elderly subjects when the posture is changed from SIT to STD, while each response is same between the young and elderly in STD, and (3) the effect of aging on the posture-related stretch reflex differs in the SOL and TA muscles.

Coordination modes in sensorimotor synchronization of whole-body movement: a study of street dancers and non-dancers.

This study investigated whole-body sensorimotor synchronization (SMS) in street dancers and non-dancers. Two kinds of knee bending movement in a standing position to a metronome beat were explored in terms of stability under different movement frequencies: down-movement condition (knee flexion on the beat) and up-movement condition (knee extension on the beat). Analyses of phase relation between movement and beat revealed several distinct differences between the down- and up-movement conditions, and between dancers and non-dancers. In both groups under the up-movement condition, deviation from intended phase relation at higher beat rates, and enhanced fluctuations were observed. The deviation from intended phase relation under up-movement condition, and movement fluctuations were greater in non-dancers than in dancers. Moreover, subjective difficulty rating revealed that both groups felt that the up-movement condition was more difficult at higher beat rates. These findings suggest that down and up movements are two distinguishable coordination modes in whole-body coordination, and that street dancers have superior whole-body SMS ability.

Traits and cognitions of perfectionism and their relation with coping style, effort, achievement, and performance anxiety in Japanese musicians.

Research has shown that 2 major facets of perfectionism can be differentiated: perfectionistic strivings and perfectionistic concerns. In order to investigate how these different facets of perfectionism are related to coping, effort, achievement, and performance anxiety in musicians, we asked 275 professional and amateur Japanese musicians to complete measures of perfectionism traits, perfectionism cognitions, coping style, effort, achievement, and performance anxiety. While both facets of perfectionism showed a similar pattern of correlation with coping measures, they were differently associated with effort, achievement, and performance anxiety. In addition, results of hierarchical regression analysis showed the incremental validity of perfectionism cognitions in explaining variance in performance anxiety above the variance explained by other variables, such as trait perfectionism. These findings demonstrate that perfectionism in musicians has both positive and negative elements.

Intrinsic constraint of asymmetry acting as a control parameter on rapid, rhythmic bimanual coordination: a study of professional drummers and nondrummers.

Expert musicians show experience-dependent reduced asymmetry in the structure of motor-related brain areas and in the maximum tapping frequency between the hands. Therefore we hypothesized that a reduced hand-skill asymmetry is strongly related to rapid and rhythmical bimanual coordination and developed a dynamical model including a symmetry-breaking parameter Δω, for human bimanual coordination. We conducted unimanual and bimanual drumming experiments to test the following model predictions. 1) The asymmetry in the maximum tapping frequency is more pronounced in nondrummers than that in drummers. If so, 2) a larger number of phase wanderings (i.e., succession of taps by the same hand), 3) larger SD of the relative phase between the hands (SD ), and 4) larger deviation of mean relative phase (mean ) from 180° would be observed in nondrummers than that in professional drummers during antiphase bimanual drumming at the maximum speed. In a unimanual tapping task, the asymmetry in maximum tapping frequency of nondrummers was more pronounced than that of professional drummers. In a bimanual coordination task, phase wanderings were observed only in nondrummers and SD of the nondrummers is significantly larger than that of professional drummers. On the other hand, there was no significant difference between the mean of the two groups. All these observations were successfully reproduced by changing Δω, which corresponded to the asymmetry in the maximum tapping frequency. These results support the hypothesis indicating that the prominent bimanual coordination pattern emerges spontaneously after a nonspecific change in Δω or symmetry restoration of the nonlinear dynamical systems.

Variability and fluctuation in running gait cycle of trained runners and non-runners.

The current study examined variability and fluctuation in the running gait cycle, focusing on differences between trained distance runners and non-runners. The two groups of participants performed treadmill running at 80%, 100%, and 120% of their preferred speed for 10 min. Stride-interval time-series were recorded during running using footswitches. The average preferred speed was significantly higher for the trained runners than for the non-runners. The trained runners showed significantly smaller variability of stride interval than did the non-runners, and at the same time the scaling exponent alpha evaluated by detrended fluctuation analysis tended to be smaller for the trained runners. These results suggest that expert runners can reduce variability in the trained movement without loosing dynamical degrees of freedom for spatiotemporal organization of the gait pattern.

Age-related changes of the stretch reflex excitability in human ankle muscles.

The purpose of this study was to characterize the effects of aging on the stretch reflex in the ankle muscles, and in particular to compare the effects on the ankle dorsi-flexor (tibialis anterior: TA) and the plantar-flexor (soleus: SOL). Stretch reflex responses were elicited in the TA and SOL at rest and during weak voluntary contractions in 20 elderly and 23 young volunteers. The results indicated that, in the TA muscle, the elderly group had a remarkably larger long-latency reflex (LLR), whereas no aging effect was found in the short latency reflex (SLR). These results were very different from those in the SOL muscle, which showed significant aging effects in the SLR and medium latency reflex (MLR), but not in the LLR. Given the fact that the LLR of the TA stretch reflex includes the cortical pathway, it is probable that the effects of aging on the TA stretch reflex involve alterations not only at the spinal level but also at the cortical level. The present results indicate that the stretch reflexes of each of the ankle antagonistic muscles are affected differently by aging, which might have relevance to the neural properties of each muscle.

Wrist muscle activity during rapid unimanual tapping with a drumstick in drummers and nondrummers.

This study investigated performance and wrist muscle activity during rapid-repetitive unimanual tapping with a drumstick in right-handed drummers and nondrummers. Analyses of performances revealed no difference in tapping frequency and peak tap force between drummers and nondrummers, although the drummers showed less variability in intertap interval than the nondrummers. Analyses of the electromyographic (EMG) data obtained by recording the activity of the flexor carpi ulnalis and the extensor carpi radialis muscles of the right wrist revealed several distinct differences between the two groups: the drummers showed a lower level of muscle cocontraction together with an earlier decline of wrist flexor muscle activity and a smaller variability of muscle activation time in the wrist flexors compared with the nondrummers. We suggest that these characteristics in wrist muscle activity in the drummers have been acquired following extensive practice for the efficient use of wrist muscles and stable drumming performance.

Motor/autonomic stress responses in a competitive piano performance.

The present study examined the effects of psychological stress on performance quality, autonomic responses, and upper extremity muscle activity in skilled pianists through comparisons between stressful (competition) and nonstressful (rehearsal) conditions. We observed increased levels of subjective anxiety, autonomic arousal, and electromyographic activity in the competition condition, which could contribute to the impairment of performance quality. The results provide important practical implications for enhancing performance quality as well as preventing playing-related musculoskeletal disorders in musicians.

Music performance anxiety in skilled pianists: effects of social-evaluative performance situation on subjective, autonomic, and electromyographic reactions.

Music performance anxiety (MPA), or stage fright in music performance, is a serious problem for many musicians, because performance impairment accompanied by MPA can threaten their career. The present study sought to clarify on how a social-evaluative performance situation affects subjective, autonomic, and motor stress responses in pianists. Measurements of subjective state anxiety, heart rate (HR), sweat rate (SR), and electromyographic (EMG) activity of upper extremity muscles were obtained while 18 skilled pianists performed a solo piano piece(s) of their choice under stressful (competition) and non-stressful (rehearsal) conditions. Participants reported greater anxiety in the competition condition, which confirmed the effectiveness of stress manipulation. The HR and SR considerably increased from the rehearsal to competition condition reflecting the activation of sympathetic division of the autonomic nervous system. Furthermore, participants showed higher levels of the EMG magnitude of proximal muscles (biceps brachii and upper trapezius) and the co-contraction of antagonistic muscles in the forearm (extensor digitorum communis and flexor digitorum superficialis) in the competition condition. Although these responses can be interpreted as integral components of an adaptive biological system that creates a state of motor readiness in an unstable or unpredictable environment, they can adversely influence pianists by disrupting their fine motor control on stage and by increasing the risk of playing-related musculoskeletal disorders.

Enhanced excitability of the corticospinal pathway of the ankle extensor and flexor muscles during standing in humans.

The purpose of this study was to investigate how the recruitment properties of the corticospinal pathway are modulated in the soleus (SOL) and tibialis anterior (TA) muscles depending on postures. A wide range of stimulus intensities were applied via transcranial magnetic stimulation over the primary motor cortex during standing (STD) and sitting (SIT) with a comparable background activity level in each muscle. The relationship between the stimulation intensities and the size of motor-evoked potentials was assessed by the Boltzmann sigmoid function, which is characterized by a plateau value, maximum slope, and threshold. The plateau value and maximum slope were significantly higher during STD than during SIT in the SOL muscle (STD vs. SIT, plateau value: 50.0 +/- 21.8 vs. 33.9 +/- 12.3 mV ms, maximal slope: 1.6 +/- 0.7 vs. 1.2 +/- 0.5 mV ms/% maximal stimulator output). Similar changes of the parameters were also observed in the TA muscle (STD vs. SIT, plateau value: 71.0 +/- 22.9 vs. 41.4 +/- 16.1 mV ms, maximal slope: 5.0 +/- 2.0 vs. 2.5 +/- 0.7 mV ms/% maximal stimulator output). The threshold did not differ significantly between the two conditions and both muscles. These results indicate that the central nervous system requires a different control for each postural condition; that is, the relative balance of the excitatory and inhibitory inputs to the corticospinal pathways as well as the number of neurons of subliminal fringe in the corticospinal pathway was increased during STD compared with those during SIT.

Tapping performance and underlying wrist muscle activity of non-drummers, drummers, and the world's fastest drummer.

Studies of rapid unimanual tapping have assumed that the human rate limit for voluntary rhythmic movement is 5-7 Hz, which corresponds to an inter-tap interval (ITI) of 150-200ms. In fact, the winner of a recent contest to find the world's fastest drummer (WFD) can perform such movements using a handheld drumstick at 10 Hz, which corresponds to an ITI of 100 ms. Because the contest measured only the number of taps by the WFD, we examined the stability of the ITI and the underlying wrist muscle activity of the WFD. By comparing the performance and wrist muscle activity of the WFD with those of two control groups (non-drummers (NDs) and ordinary skilled drummers (ODs)), we found that the WFD had a relatively stable ITI and more pronounced reciprocal wrist muscle activity during the 10-Hz performance. Our result indicates that very fast, stable tapping performance can be achieved by keeping the wrist joint compliant rather than stiff.

Exploring the mechanism of skilled overarm throwing.

Although the kinematics and dynamics of overarm throws, such as baseball pitching, have been studied extensively, the relations between these measures remain largely unknown. This review uses a three-dimensional analysis to characterize the mechanical basis of skilled overarm throws by focusing on how each joint angular acceleration is produced by the muscle torques, gravity torques, and velocity-dependent torques.

Kinetic chain of overarm throwing in terms of joint rotations revealed by induced acceleration analysis.

This study investigated how baseball players generate large angular velocity at each joint by coordinating the joint torque and velocity-dependent torque during overarm throwing. Using a four-segment model (i.e., trunk, upper arm, forearm, and hand) that has 13 degrees of freedom, we conducted the induced acceleration analysis to determine the accelerations induced by these torques by multiplying the inverse of the system inertia matrix to the torque vectors. We found that the proximal joint motions (i.e., trunk forward motion, trunk leftward rotation, and shoulder internal rotation) were mainly accelerated by the joint torques at their own joints, whereas the distal joint motions (i.e., elbow extension and wrist flexion) were mainly accelerated by the velocity-dependent torques. We further examined which segment motion is the source of the velocity-dependent torque acting on the elbow and wrist accelerations. The results showed that the angular velocities of the trunk and upper arm produced the velocity-dependent torque for initial elbow extension acceleration. As a result, the elbow joint angular velocity increased, and concurrently, the forearm angular velocity relative to the ground also increased. The forearm angular velocity subsequently accelerated the elbow extension and wrist flexion. It also accelerated the shoulder internal rotation during the short period around the ball-release time. These results indicate that baseball players accelerate the distal elbow and wrist joint rotations by utilizing the velocity-dependent torque that is originally produced by the proximal trunk and shoulder joint torques in the early phase.

Control of 3D limb dynamics in unconstrained overarm throws of different speeds performed by skilled baseball players.

This study investigated how the human CNS organizes complex three-dimensional (3D) ball-throwing movements that require both speed and accuracy. Skilled baseball players threw a baseball to a target at three different speeds. Kinematic analysis revealed that the fingertip speed at ball release was mainly produced by trunk leftward rotation, shoulder internal rotation, elbow extension, and wrist flexion in all speed conditions. The study participants adjusted the angular velocities of these four motions to throw the balls at three different speeds. We also analyzed the dynamics of the 3D multijoint movements using a recently developed method called "nonorthogonal torque decomposition" that can clarify how angular acceleration about a joint coordinate axis (e.g., shoulder internal rotation) is generated by the muscle, gravity, and interaction torques. We found that the study participants utilized the interaction torque to generate larger angular velocities of the shoulder internal rotation, elbow extension, and wrist flexion. To increase the interaction torque acting at these joints, the ball throwers increased muscle torque at the shoulder and trunk but not at the elbow and wrist. These results indicates that skilled ball throwers adopted a hierarchical control in which the proximal muscle torques created a dynamic foundation for the entire limb motion and beneficial interaction torques for distal joint rotations.

A new non-orthogonal decomposition method to determine effective torques for three-dimensional joint rotation.

This paper describes a new non-orthogonal decomposition method to determine effective torques for three-dimensional (3D) joint rotation. A rotation about a joint coordinate axis (e.g. shoulder internal/external rotation) cannot be explained only by the torque about the joint coordinate axis because the joint coordinate axes usually deviate from the principal axes of inertia of the entire kinematic chain distal to the joint. Instead of decomposing torques into three orthogonal joint coordinate axes, our new method decomposes torques into three "non-orthogonal effective axes" that are determined in such a way that a torque about each effective axis produces a joint rotation only about one of the joint coordinate axes. To demonstrate the validity of this new method, a simple internal/external rotation of the upper arm with the elbow flexed at 90 degrees was analyzed by both orthogonal and non-orthogonal decomposition methods. The results showed that only the non-orthogonal decomposition method could explain the cause-effect mechanism whereby three angular accelerations at the shoulder joint are produced by the gravity torque, resultant joint torque, and interaction torque. The proposed method would be helpful for biomechanics and motor control researchers to investigate the manner in which the central nervous system coordinates the gravity torque, resultant joint torque, and interaction torque to control 3D joint rotations.

'Initial state' coordinations reproduce the instant flexibility for human walking.

An important feature of human locomotor control is the instant adaptability to unpredictable changes of conditions surrounding the locomotion. Humans, for example, can seamlessly adapt their walking gait following a sudden ankle impairment (e.g., as a result of an injury). In this paper, we propose a theoretical study of the mechanisms underlying flexible locomotor control. We hypothesize that flexibility is achieved by modulating the posture at the beginning of the stance phase-the initial state. Using a walking model, we validate our hypothesis through computer simulations.

The effect of visual transformation on bimanual circling movement.

In order to examine the effect of visual transformation on bimanual movements of various difficulty, fourteen participants performed bimanual circling tasks in three asymmetric movement modes--90 degrees (the left hand precedes the right hand by 1/4 cycle), 180 degrees (the delay between two hands is 1/2 cycle), and 270 degrees (the left hand precedes the right hand by 3/4 cycle)--under the normal vision condition and the visual transformation condition. In the visual transformation condition, movement of the right hand was transformed so that the required bimanual movement was always presented visually as a symmetric pattern. Additionally, the participants also performed a 0 degrees mode (in-phase symmetric) movement. Results revealed that the visual transformation increased the movement accuracy, with the variability of the right-left difference unchanged. Thus, proper visual transformation can improve the accuracy of a movement task. The 0 degrees mode was performed with higher stability and accuracy than any other movement modes of the visual transformation condition and normal vision conditions. In addition, the constant error associated with the 90 degrees and 270 degrees modes indicated that, in the normal vision condition, the executed movement was shifted to the 180 degrees mode, whereas in the visual transformation condition it stayed around the required mode and was slightly shifted to the 0 degrees mode. This result suggests that visual transformation can change the relationship between the intention to realize the required mode and the intrinsic neuromuscular dynamics. The effect size of visual transformation was larger in the 90 degrees and 270 degrees modes than in the 180 degrees mode. It is thus concluded that the effect of visual transformation depends upon the difficulty of the movement task.